﻿154 
  Scientific 
  Intelligence. 
  

  

  II. 
  Geology 
  and 
  Mineralogy. 
  

  

  1. 
  Note 
  on 
  the 
  Florida 
  Reef 
  ; 
  by 
  A. 
  Agassiz. 
  (Letter 
  to 
  

   J. 
  D. 
  Dana 
  dated 
  Tampa 
  Bay, 
  Florida, 
  Dec. 
  27, 
  1894)— 
  You 
  will 
  

   be 
  interested 
  to 
  hear 
  that 
  I 
  have 
  just 
  returned 
  from 
  a 
  ten 
  days' 
  

   trip 
  to 
  the 
  Florida 
  reefs, 
  which 
  I 
  was 
  anxious 
  to 
  examine 
  again, 
  

   in 
  the 
  light 
  of 
  the 
  experience 
  gained 
  by 
  my 
  visit 
  to 
  the 
  Bahamas 
  

   and 
  Bermudas 
  ; 
  I 
  think 
  I 
  shall 
  be 
  obliged 
  materially 
  to 
  change 
  

   my 
  ideas 
  of 
  the 
  mode 
  of 
  formation 
  of 
  the 
  Keys, 
  and 
  to 
  give 
  up 
  the 
  

   Marquesas 
  as 
  a 
  true 
  Atoll. 
  After 
  having 
  seen 
  at 
  the 
  Bermudas 
  the 
  

   mode 
  of 
  formation 
  of 
  the 
  Sounds, 
  I 
  have 
  become 
  satisfied 
  that 
  the 
  

   Marquesas 
  are 
  a 
  Sound. 
  But 
  the 
  Florida 
  Sounds 
  do 
  not, 
  I 
  think, 
  

   owe 
  their 
  origin 
  to 
  subsidence, 
  but 
  merely 
  to 
  the 
  mechanical 
  and 
  

   solvent 
  action 
  of 
  the 
  sea. 
  It 
  is 
  interesting 
  to 
  trace 
  on 
  the 
  large 
  

   scale 
  charts 
  of 
  the 
  Coast 
  Survey 
  the 
  mode 
  of 
  formation 
  of 
  Key 
  

   Biscayne 
  Bay, 
  composed 
  of 
  two 
  sounds, 
  followed 
  by 
  Barns 
  Sound, 
  

   and 
  finally 
  to 
  the 
  westward, 
  by 
  the 
  Bay 
  of 
  Florida, 
  itself 
  only 
  a 
  

   series 
  of 
  disconnected 
  sounds 
  indicated 
  by 
  isolated 
  keys 
  and 
  bars. 
  

   The 
  same 
  thing 
  is 
  going 
  on 
  at 
  the 
  Pine 
  Islands, 
  Key 
  West, 
  Boca 
  

   Chica, 
  Boca 
  Grande, 
  Ballast 
  Key, 
  and 
  is 
  especially 
  well 
  seen 
  in 
  

   Key 
  Largo, 
  the 
  Marquesas, 
  to 
  the 
  west 
  of 
  the 
  principal 
  line 
  of 
  Keys 
  

   being 
  a 
  remarkably 
  well 
  preserved 
  sound 
  of 
  an 
  elliptical 
  shape. 
  

   To 
  my 
  great 
  surprise 
  I 
  found 
  that 
  Lower 
  Matecumbe 
  was 
  edged 
  by 
  

   an 
  elevated 
  reef 
  about 
  2 
  feet 
  above 
  high 
  water 
  mark 
  ! 
  and 
  this 
  

   elevated 
  reef 
  I 
  was 
  able 
  to 
  trace 
  all 
  along 
  the 
  shores 
  of 
  the 
  Keys 
  

   to 
  the 
  east 
  of 
  Indian 
  Key 
  as 
  far 
  as 
  Soldiers 
  Key, 
  off" 
  the 
  central 
  

   part 
  of 
  Key 
  Biscayne. 
  I 
  examined 
  this 
  elevated 
  reef 
  also 
  at 
  

   Indian 
  Key 
  where 
  its 
  highest 
  point 
  is 
  8 
  feet 
  above 
  high 
  water 
  

   mark, 
  at 
  several 
  points 
  on 
  Key 
  Largo, 
  Old 
  Rhodes, 
  Elliott 
  Key, 
  

   and, 
  as 
  the 
  most 
  easterly 
  point, 
  Soldiers 
  Key. 
  No 
  trace 
  of 
  this 
  

   elevated 
  reef 
  could 
  be 
  detected 
  north 
  of 
  Cape 
  Florida, 
  Key 
  Bis- 
  

   cayne 
  being 
  entirely 
  covered 
  by 
  siliceous 
  sands, 
  just 
  as 
  the 
  beaches 
  

   of 
  limestone 
  sands 
  cover 
  great 
  tracts 
  of 
  the 
  Keys 
  to 
  the 
  westward 
  

   and 
  hide 
  the 
  underlying 
  elevated 
  reef. 
  Shaler 
  speaks 
  of 
  having 
  

   traced 
  this 
  reet 
  at 
  Old 
  Rhode's 
  and 
  having 
  followed 
  it 
  to 
  the 
  Miami 
  

   River 
  as 
  an 
  elevated 
  reef. 
  I 
  was 
  quite 
  surprised 
  on 
  examining 
  a 
  

   bluff 
  about 
  ten 
  feet 
  in 
  height, 
  extending 
  eastward 
  from 
  Cocoanut 
  

   Point 
  toward 
  the 
  mouth 
  of 
  the 
  Miami 
  River, 
  to 
  find 
  that 
  it 
  con- 
  

   sisted 
  of 
  ceolian 
  rocks 
  which 
  have 
  covered 
  the 
  elevated 
  reef 
  in 
  

   many 
  places. 
  On 
  the 
  low 
  shores 
  these 
  seolian 
  rocks 
  are 
  honey- 
  

   combed 
  and 
  pitted 
  and 
  might 
  be 
  readily 
  mistaken 
  for 
  decomposed 
  

   reef 
  rocks; 
  but 
  they 
  contain 
  no 
  corals. 
  This 
  looks 
  as 
  if 
  the 
  lower 
  

   southern 
  extremity 
  of 
  Florida, 
  the 
  Everglade 
  tracts, 
  was 
  a 
  huge 
  

   sink 
  into 
  which 
  sands 
  had 
  been 
  blown 
  forming 
  low 
  dunes 
  which 
  

   have 
  little 
  by 
  little 
  been 
  eroded, 
  and 
  which 
  former 
  observers 
  had 
  

   mistaken 
  in 
  some 
  localities 
  for 
  reef 
  rock. 
  The 
  material 
  for 
  these 
  

   dunes 
  coming 
  from 
  the 
  (now 
  elevated) 
  reef 
  at 
  a 
  time 
  when 
  it 
  was 
  

   either 
  a 
  fringing 
  or 
  a 
  barrier 
  reef 
  along 
  the 
  former 
  coast 
  line 
  of 
  

   Florida, 
  all 
  of 
  which, 
  back 
  of 
  the 
  reef, 
  has 
  little 
  by 
  little 
  been 
  eroded 
  

  

  